Engines which are required to operate under severe conditions of high temperatures for extended periods of time need a high performance lubricant that can withstand the extreme conditions. High performance lubricants will not degrade under high temperatures and will have a relatively small change in viscosity over a wide temperature range; that is, a high viscosity index.
Attempts to thermally polymerize various 1-olefins have been described. For example, U.S. Pat. No. 2,500,166 teaches a synthetic lubricating oil made from mixtures of normally liquid straight-chain 1-olefins containing from six to twelve carbon atoms by thermal treatment of the olefins. The thermal treatment includes polymerization of 1-decene at 190.degree.-440.degree. C. for 1 to 40 hours and non-critical pressures of reaction ranging from less than 50 to over 1000 pounds per square inch of pressure. The patent identifies as conditions, for good yields of good products, polymerization at a range from 3 to 20 hours and at temperatures of from about 650.degree. F. (330.degree. C.) to about 600.degree. F. (300.degree. C.). The patent teaches that increased pressure is desirable to maximize the yield. Although a high yield is beneficial to refinery operation, the detriment of running a reactor at high pressures can outweigh the benefit of a greater yield.
A 2-stage thermal polymerization of mixed mono-olefins is taught in U.S. Pat. No. 3,883,417. The product is first polymerized under pressure conditions ranging from atmospheric to 1000 psig at temperatures ranging from 300.degree. F. to 650.degree. F. The product is distilled to 600.degree.-650.degree. F. to obtain a purified product which is treated in a second-stage polymerization at 600.degree.-800.degree. F. and at 0 to 1000 psig. The unreacted olefins of the second stage polymerization can be distilled off and recycled to the second-stage polymerization. Although the products resulting from the 2-stage thermal process have a good VI, a higher VI product made by a one-stage thermal process would be desirable.
In general, premium lubricating oils are finished by hydrogen finishing (hydrofinishing) units which eliminate the polar sites in the oil molecules and improve their thermal stability and oxidation stability and lighten their color.
In the hydrofinishing unit the charge oil is first heated, mixed with hydrogen, and then heated again to a temperature sufficient to effectuate reaction. The heated charge is pumped into the reactor which contains a hydrotreating catalyst. The reaction destroys the molecular polarity and lightens the color of the oil.